Sciences des matériaux

Nombre total de résultats : 417
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Elaboration et caractérisation de céramiques ZnO-TiO2.

Alima MEBREK (2018)
Thèse de doctorat

L'orthotitanate de zinc (Zn2TiO4) de structure spinelle inverse a été préparée par la méthode solide en deux étapes. La première étape consiste à broyer mécaniquement un mélange de poudres de ZnO et TiO2 avec un rapport molaire de 2:1 dans un broyeur planétaire à haute énergie sous atmosphère d'argon. Les poudres broyées ont été ensuite calcinées à 900°C pendant 2 heures, puis pressées en pastilles et frittées pendant 4 heures à 1100°C à l'air. La formation des phases, la microstructure, la morphologie de surface et les propriétés optiques ont été étudiées par diffraction des rayons X, spectroscopies Raman, infrarouge à transformée de Fourier (FT-IR), microscopie électronique à balayage couplée à la spectroscopie à rayons X à dispersion d'énergie (EDX), microscopie à force atomique et spectrophotométrie UV/visible. Les résultats des rayons X de la poudre broyée pendant 6 h révèlent la présence de Zn2TiO4 nanocristallin (15,5 %, = 13,2 nm), en plus de l'anatase a-TiO2, ZnO et le rutile r-TiO2. La fraction volumique de la phase Zn2TiO4 augmente avec le temps de broyage. Les pastilles présentent une structure composite dans laquelle une petite quantité de nanograins de rutile r-TiO2 est dispersée dans la matrice de titanate de zinc Zn2TiO4. Les résultats des spectroscopies FT-IR et Raman confirment le caractère biphasique des pastilles. La microstructure de la pastille 18 h est assez propre avec une répartition homogène de la taille des grains par rapport à celle de la pastille 6 h qui présente peu de pores. La rugosité de surface (r.m.s) des pastilles diminue avec l'augmentation du temps de broyage. L'énergie de la bande interdite des pastilles 6 h et 18 h est de l'ordre de 3,22 eV et 3,45 eV, respectivement. Voir les détails

Mots clés : Broyage mécanique, Système ZnO-TiO2, DRX, SEM

Preparation and characterization of spinel type Zn2TiO4 nanocomposite.

Alima MEBREK, Safia ALLEG, Sihem BENAYACHE, Mohamed BENABDSLEM  (2018)

Zinc orthotitanate Zn2TiO4 spinel structures have been prepared by solid state reaction in two stages. First, a mixture of ZnO and TiO2 (67% anatase+33% rutile) in a molar ratio of 2:1 was mechanically milled for 6 and 18 h, at room temperature, in a high energy planetary ball mill under argon atmosphere. Next, the ball milled powders were calcined at 900°C for 2 h, pressed into pellets and then sintered for 4 h at 1100°C in air. Phase formation, microstructure, surface morphology and optical properties were characterized by X-ray di?raction, Raman scattering spectroscopy, Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy coupled with energy dispersive X-ray spectroscopy, atomic force microscopy and UV–visible spectro- photometery. The mechanical milling process for 6 h gives rise to the formation of nanocrystalline orthotitanate Zn2TiO4 (15.5%, =13.2 nm) in addition to unreacted rutile TiO2, anatase TiO2 and ZnO structures. As the milling process progresses up to 18 h, the volume fraction of Zn2TiO4 increases to about 44.5%. The sintered pellets exhibit a composite structure where about a small amount of rutile nanograins are dispersed into the Zn2TiO4 matrix. FT-IR and Raman results con?rm the biphasic character of the sintered pellets. The band gap energy is milling time dependent. It varies from 3.22 for pellet 6 h to 3.45 for pellet 18 h. Voir les détails

Mots clés : Mechanical Alloying, ZnO−TiO2 system, XRD, Raman spectroscopy, SEM

Experimental study of the thermo-mechanical behaviour of alumina-silicaterefractory materials elaborated from Algerian kaolinitic clays

A.GRID, N. TOUATI, S. LADJAMA, A. Mebrek, H.Rezzag, S.Bouchoucha  (2018)
Article de conférence

This work aims to study the thermomechanical behavior of an algerian kaolinitic clay. We started with the characterization of the raw material (DD1) of Djebel Debbagh -Guelma, in order to obtain a deep information about the microstructure of the material before and after a heat treatment, notably its crystallographic nature and the grains size and shape. The chemical composition and physical properties are reported. The mineralogical and chemical characteristics, based on X-ray diffraction (XRD) and scanning electron microscopy (SEM), were also carried out. The general behavior of the material with increasing temperature was analyzed through the various microstructure investigations and thermal analysis. Voir les détails

Mots clés : Thermo-mechanical properties, aolinitic clays, elaborate

Puzzle of c-WN phase stabilization

W. RICHI, D. ZANATI  (2018)
Article de conférence

In this paper, we present first-principles calculationsthat compare structural and electronic properties of WN inthe NaCl and NbO phases. Our results predict that the NbOstructure of WN is more stable than the NaCl structure withoutdefects, where the enthalpy of formation per formula unit Hf =-0.872eV and 0.616eV for NbO and NaCl structures, respectively.Moreover, the calculated lattice parameters of c-WN are a=4.35A°and a=4.11A° for NaCl and NbO phases, respectively. It is veryclear that the lattice parameter obtained for c-WN in NbO is invery good concordance with that reported experimentally of a =4.14A° . Although the formation energy calculations support thehypothesis of the stability of the NbO phase, the experimental xrayphotoelectron spectroscopy (XPS) electron density of statesfor valence band spectra corresponds to that density of statescalculated for c-WN in NaCl phase. Based on this comparison,more consideration must be taken into account to elucidate thisissue. Voir les détails

Mots clés : Cubic Tungsten nitride ceramics, Firstprinciples calculations, Formation energy


A. Azzi, L. Bahloul, L. Alimi, S. Guerfi, S. Bouyeg, M. Boulkra, A. Grairia  (2018)
Article de conférence

The objective of this work is the elaboration of a biomaterial Hydroxyapatite (Ca10 (PO4)6 (OH)2), by a synthetic method of precipitation, (CaCl2, 2H2O) as source of calcium and (Na2HPO4, 12 H2O) as a source of phosphate. After preparation, the powder was calcined at 900 °C for 90 minutes at a speed of 10 °C / min and compacted into pellets 12 mm in diameter and 2 mm thick. Sintered powder at different temperatures (1000 °C, 1100 °C, 1200 °C, and 1300 °C). In order to study the effect of sintering temperature on the microstructure, the physical and morphological properties of the elaborated hydroxyapatite, the density, the porosity, X-ray diffraction (DRX) and the scanning electron microscopy (SEM) were used for the characterization of the powder. The density decreases with the increase of the porosity, in fact the sample densifies easily when the porosity is lower Voir les détails

Mots clés : hydroxyapatite, SEM, DRX, Porosity, Density

Electroless copper deposition on epoxy glass substrate for electrocatalysis of formaldehyde

C. Dehchar, I. CHIKOUCHE, R. KHERRAT, A. Sahari, A. Zouaoui, A. MERATI  (2018)

In this paper, we investigated the characteristics of a structured copper (Cu) ?lm deposited on the surface of an insulating epoxy glass (EG) substrate via a facile electroless plating process. The ?lm produced by this method was found to be of high purity and has a homogeneous microstructure consisting of an assembly of numerous aggregates that vary in size from 1 to 5 mm depending on the electroless deposition time. The electrocatalytic activity of the prepared electrode was investigated for the electrooxidation of formaldehyde using cyclic voltammetry in 0.1 M NaOH solution. Results show that formaldehyde oxidation takes place at a low potential of -0.34 V with large anodic current densities. Voir les détails

Mots clés : copper, electroless plating, Formaldehyde, Oxidation, Thin films

Proposition of a mechanical model to predict the behaviour of a laminate bio composite material

D.ZELMATI, W.Ghelloudj, K.BEDOUD, M.HASSANI  (2018)
Article de conférence

The purpose of this paper is to develop a mechanical model able to predict the mechanical behaviour of a laminate bio-composite material reinforced by the flax fibres without necessity to the expensive experimental test. A numerical comparative modelling based on finite element method is conducted by using in one hand a several stacking sequences, and in the other hand a growing plies number in order to estimate the lateral deflexion U3 in each plies of the bio-composite subjected to compression load. Meanwhile, the proposed mathematical model can be used as a power tool decision in design and the ensuring of the structure integrity. Voir les détails

Mots clés : Bio-composite, laminate, flax, modeling

Structure, magnetic and microwave studies of mechanically alloyed powders Fe45Ni35Co20

Ahmed HADDAD, Insaf Ouldbrahim, Mohamed Azzaz  (2018)

Nanocrystalline Fe-35 wt%Ni-20 wt%Co has been prepared by using a high-energy planetary ball mill with increasing milling time from 4 to 36 h. Microstructural characterisations showed the development of an face-centred cubic nanostructured Fe-35 wt%Ni-20 wt%Co alloy with an average crystallite size of 8 nm. The magnetic investigation revealed that the nanostructures obtained from a milling time of 36 h have the highest magnetic saturation and the lowest coercive field. In addition, the hardness and the electromagnetic absorption of the Fe-35 wt%Ni-20 wt%Co alloy were found to increase with the milling time. These evolutions could be attributed to the crystallite size and the strain variations in the samples during milling. Voir les détails

Mots clés : nanostructure, magnetic, nanocristalline, Mechanical Alloying, Fe, Co

Electrocatalytic oxidation of ascorbic acid at polypyrrole thin film incorporating palladium particles

Charif DEHCHAR, Imene CHIKOUCHE, Rochdi KHERRAT, Saida ZOUGAR, Ahmed ZOUAOUI  (2017)

In this paper, we report a simple sensing strategy for electrochemical determination of ascorbicacid (AA) using a combination of polypyrrole (PPy) thin film and palladium particles composites deposited onto n-doped silicon (Si) substrate. A two-step electrochemical process was employed to synthesize the composite films: At first, PPy film (average thickness 200 nm) was electro-generated on Si substrate from an organic solution of the pyrrole under galvanostatic conditions. Secondly, palladium particles were electrodeposited on PPy/Si surface from a separate solution by chronoamperometry technique. The surface morphology analysis of the obtained composites shows a uniform dispersion of palladium particles onto the polymer matrix and reveals that the electrodeposition time has a significant effect on the amount and size of the incorporated palladium particles. The electrochemical reactivity of the Pd–PPy/Si-modified electrodes towards the oxidation of AA was studied by cyclic voltammetry method in 0.1 M, pH 7.0 phosphate buffer solution. The oxidation current was proportional to the concentration of AA in the range of 0.5–10 mM with a detection limit of 0.2 mM. Voir les détails

Mots clés : ascorbic acid, composite, electrocatalysis, Electropolymerization, palladium, Polypyrrole

Microstructure, Corrosion and Magnetic Behavior of an Aged Dual-Phase Stainless Steel

A. Ziouche, A. Haddad, R. Badji, M. Zergoug, N. Zoubiri, W. Bedjaoui, S. ABAIDIA  (2018)

In the present work, the effect of the precipitation phenomena on corrosion and magnetic behavior of an aged dual-phase stainless steel was investigated. Aging treatment caused the precipitation of the σ phase, chromium carbides and secondary austenite, which was accompanied by the shifting of the δ/γ interfaces inside the δ ferrite grains. Aging between 700 and 850 °C strongly deteriorated the pitting corrosion resistance of the studied material. Magnetic investigation of the aged material using the vibration sample magnetic technique revealed the sensitivity of the intrinsic magnetic properties to the smallest microstructural change. This was confirmed by the Eddy current technique that led also to the evaluation of the aging-induced localized corrosion. Voir les détails

Mots clés : σ phase, aging treatment, DSS, Magnetic Properties, microstructure, Pitting corrosion